1. Field of the Invention
The invention relates to a transparent antireflection (AR) coating having antistatic properties, an optical article coated with such coating and a method of manufacturing such optical article.
2. Description of Related Art
Organic lenses have a tendency to get charged, especially when they are cleaned in dry conditions with a cloth and consequently they may attract dusts during the time the charge remains on the lens.
It is known in the art to include at least one electrically conductive layer inside an antireflection stack in order to confer to the antireflection coated lens antistatic properties. This helps in quickly dissipating the charges.
For example, International Patent Application WO 01/55752 describes substrates coated with an AR stack including an electrically conductive layer having a sheet resistance (i.e. a surface resistivity) of 1.107 to 1.1010 ohm/square. Such electrically conductive layer can be positioned at different locations of the AR stack. Practically, the conductive layer is made of a material selected from the group comprising oxides of indium, tin and zinc. Only two materials are described, indium tin oxide (ITO) and tin oxide, the preferred one being the former. The AR coating including the conductive layer can be deposited by sputtering or by vacuum evaporation deposition.
As known in the art, when depositing by vacuum evaporation the ITO layer, it is recommended to use ion assistance (IAD) in order to increase transparency. This additional step has at least two disadvantages: i) The vacuum coaters including an ion gun are more expensive; and ii) The process using IAD implies sometimes problems of reproducibility.